CRANSTON, R.I. — If Rhode Island is to eradicate the ominously named invasive plant known as mile-a-minute vine, the contents of Lisa Tewksbury’s Igloo cooler will be the key.

CRANSTON, R.I. — If Rhode Island is to eradicate the ominously named invasive plant known as mile-a-minute vine, the contents of Lisa Tewksbury’s Igloo cooler will be the key.

She lugs the battered red-and-white container through a field between Route 37 and Phenix Avenue on a recent morning, leading the way through raspberry brambles, waist-high foxtail and dense clumps of milkweed and goldenrod before reaching her destination: a thick tangle of mile-a-minute, an aggressive weed originally from East Asia that grows up to 6 inches in a day and as much as 20 feet in a summer and can choke out native plants.

Tewksbury, a University of Rhode Island entomologist, opens the cooler and pulls out one of five pint-size containers with mesh-lined air holes in their lids. She pries off the lid and gently takes out a damp paper towel flecked with a couple hundred little black insects.

Tewksbury holds one out in the palm of her hand. This is rhinoncomimus latipes, more commonly called the mile-a-minute weevil, so named because it feeds exclusively on the mile-a-minute vine.

The weevil, which also originates in Asia, is tiny and could almost be mistaken for a tick. But upon closer inspection, its flexible snout, which all weevils have, can just be seen.

Tewksbury drops the insect onto the triangle-shaped leaf of a mile-a-minute vine and then uses a soft-tipped paintbrush to move the other weevils off the paper towel and onto other plants.

“People are often let down,” she says with a laugh as she works. “It’s really just releasing insects.”

It may indeed be a little underwhelming, but Tewksbury knows how important it is for the weevils to take to their new home — and feeding ground.

“Without this, the vine would just continue to grow and expand,” she says.

History of the vine

Persicaria perfoliata, or mile-a-minute vine, was first discovered in the United States in the 1930s. It’s not known for certain how it got here. The vine is native to China, Japan, Indonesia and other Asian countries. One theory is that the vine’s seeds were accidentally mixed in with a batch of holly seeds that were shipped from Japan to the United States.

Over the past 80 years, the prickly vine has quickly proliferated, taking over fields and climbing up trees in the District of Columbia and 10 states in the mid-Atlantic and New England.

It was first seen in Rhode Island in 2008 in Cranston and has since been found in Hopkinton and East Greenwich and on Block Island.

The vine produces berries containing seeds that birds and deer eat. The animals move on and the seeds pass through their system, often intact. One study found that 40 percent of mile-a-minute seeds survived ingestion by deer unharmed.

The vine is an annual, meaning it dies back in the winter. But each plant produces many seeds, so when the weather warms in the summer the vine spreads with new shoots. Cutting it back is often just a temporary fix, because mile-a-minute seeds will survive up to six years in the soil.

Although Japanese beetles, which are common in New England, eat mile-a-minute and some caterpillars do too, they are not as effective in controlling the vine as mile-a-minute weevils, which are native to China.

That’s mainly because the weevils eat nothing but the vine. Adults feed on the vine’s leaves, drawn especially to the tender new growth at the top. They lay their eggs on the stem, and when the larvae hatch, they bore into the stem and eat it, preventing the plant from flowering and producing seeds.

That was what drew researchers in Delaware and New Jersey to the weevil in 1996, when they started looking at ways to stop the spread of mile-a-minute vine.

After extensive testing to ensure that mile-a-minute weevils wouldn’t eat native plants, the U.S. Department of Agriculture approved the use of the insects in 2004. They were first released in Delaware and subsequently in New Jersey, Maryland, Pennsylvania and West Virginia.

The weevils were introduced in Rhode Island in 2009. Those early batches of insects were raised at a lab in New Jersey, but as demand increased as the fight against mile-a-minute spread to other states, URI decided to rear its own.

The lab started releasing its weevils in 2011. It produces 18,000 weevils each summer. Most are released in Rhode Island but the lab has also sent some to Connecticut and Massachusetts.

URI lab

Invasive plants can displace native species, throwing ecosystems off balance. It’s not only plants that suffer. Animal populations can also be disrupted when their habitats change. And some plants, such as garlic mustard, can have a negative effect on soil quality.

Biological control — in essence, reuniting natural predators with their prey — is growing more common as an alternative to pesticides or herbicides to stop invasive species.

In Rhode Island, the work is centered at URI’s Biological Control Lab, which is directed by entomology Prof. Richard Casagrande and managed by Tewksbury. The lab started working in earnest on invasive species projects after building a quarantine facility in 1994.

Because of the potential to cause unintentional damage by introducing non-native insects to the area, research on any one project can take up to a decade.

“Biocontrol has benefits in not using chemicals,” says Tewksbury. “But there are concerns. Once you introduce something, you can’t undo it. That’s what is talked about all the time.”

One of the early uses of biocontrol by the lab was the introduction in 1994 of the Galerucella beetle to battle the spread of purple loosestrife, an invasive plant that can grow up to 8 feet tall and is known to clog waterways.

The beetles successfully devoured thickets of loosestrife that had taken over the wetlands exhibit at Roger Williams Park Zoo, allowing native elderberry and marsh marigolds to return. The insects have been used in other parts of the state since.

More recently, the lab started releasing parasitic flies to kill off winter moths, invaders from Europe that defoliate trees and can cause particular harm to blueberry and apple farms. The fly, Cyzenis albicans, lays its eggs on tree leaves and when the moth caterpillars eat the leaves, they ingest the eggs, too. The eggs hatch and the fly larvae grow inside the caterpillars and consume them from the inside.

The lab has also used French wasps in much the same way to kill off lily-leaf beetles, which can strip lilies of all their leaves, and is exploring the use of a weevil that eats knapweed and the use of Archanara moths to control the spread of phragmites.

The lab is in the midst of finalizing research on introducing a type of moth to control swallow-wort vine, a European plant that is also crowding out native vegetation. Hypena opulenta caterpillars, which feed on swallow-wort leaves, have been approved for use in Canada but not yet in the United States. Tewksbury expects to be awarded a permit to begin releasing the moth in 2015.

She points to the work done on swallow-wort to explain the rigor of biocontrol research. The URI lab has had to prove that the caterpillars it is raising will only eat swallow-wort and not damage endemic species.

“We tested them out on 80 species of native plant,” she says. “You can’t just do two or three.”

A thousand a week

On this day, Tewksbury releases 1,100 weevils in the field in Cranston. She will release another thousand a week over the rest of the summer.

This may be the last year that she raises weevils. The hope is that the insects in the wild will reproduce enough to sustain their population and keep mile-a-minute in check.

[weevil-closeup]

She and students from the Biocontrol lab will continue to regularly check 10 monitoring stations to see how the weevils are faring. They count the number of weevils and the number of new stems on mile-a-minute plants. They also rate the damage to the vine’s leaves.

But even if the weevils can just curtail the spread of mile-a-minute, it may be enough. Native plants may be able to return and provide enough competition to keep the invasive vine in check. Researchers in Delaware have had some early success planting goldenrod to crowd out mile-a-minute once the weevils did their part.

Tewskbury checks one monitoring station. She can see many weevils on the vines and their hole-pocked leaves. Because of the hungry insects, the plants have few flowers and fewer seedpods.

That may be a sign that Rhode Island is winning the war against mile-a-minute vine.